A replacement metal gate (RMG) flow is a process to form metal gates. The process includes, for example, forming a dummy or sacrificial gate structure on a substrate, and thereafter removing the dummy or sacrificial gate structure to form the permanent metal gate structure.
In a high-k last process, channel stress materials, e.g., Ge, SiGe or SiC, can be first formed on the substrate, followed by deposition of sacrificial layers, e.g., dummy oxide, and dummy gate material, e.g., poly silicon. After the stress materials and sacrificial layers are deposited, they are then patterned to form discrete structures. Subsequent process flows include the formation of source and drain regions, and the removal of the sacrificial layers to form trenches. A metal gate process can then be performed, by depositing a high-k material within the trench and thereafter a metal material, or combinations of metal materials, to form the high-k metal gate structure. However, in such conventional RMG flows, the channel stress material, e.g., Ge, SiGe or SiC, becomes damaged or impaired due to the processing conditions in the subsequent process flows. This, in turn, will impair device performance. More specifically, thermal processes and implant processes, which include being exposed to different environment conditions such as temperature, pressure and gas, when forming and patterning of the sacrificial layers, will affect the quality of the channel stress material and its properties. Also, the removal of the sacrificial layers through etching processes are also known to attack the stress materials, which will also affect its qualities and its properties.
In a high-k first process, the RMG flow includes forming a high-k dielectric material on a substrate through a conventional deposition or growth process. A sacrificial material is then formed on the high-k dielectric material to form the dummy gate structure. The high-k dielectric material and the sacrificial material are then patterned to form discrete structures. Channel stress materials can be formed in the substrate to increase device performance. The stress materials can be, for example, Ge, SiGe or SiC. The channel stress materials can be formed prior to the deposition of the high-k material, or after the patterning process, depending on the process flow. In either scenario, the channel stress materials can be formed in the channel region or on the sides of the channel regions through a deposition or growth process. Thereafter, source and drain regions are formed in the substrate, through a doping or implantation process. The source and drain can also be formed using a doped epitaxial process. Subsequent process flows include the removal of the sacrificial material to form trenches. In this process, the channel material remains within the trenches. However, in such conventional RMG flows, the channel material, which may include the stress material, becomes damaged or impaired due to the processing conditions, similar to that discussed above. This, in turn, will impair device performance.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.